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Hey Guys,
I am working on a short scale bass and have the neck nearly done but have an issue with the truss rod not working as planned. This is the first electric guitar neck I have ever made from scratch so not sure what the problem is.

You can see in the pic below it is a "Fender" style 3 piece laminated neck made of maple.
It has a 28" StewMac low profile truss rod.

I installed the rod, glued the fretboard on (being careful not to glue the rod in)

Shaped the headstock and cut the access hole.

BUT... Adjusting the truss rod barely moves the neck...

I have NOT shaped the back of the neck yet and am wondering if the neck is just too thick to have the rod work?

I am reluctant to shape the back in case I need to remove the fretboard.

Any help or advice is welcome,

Thanks,
Bob

"I have NOT shaped the back of the neck yet and am wondering if the neck is just too thick to have the rod work?"

Probably yeah.

It won't be any more difficult to remove the fretboard with the necks shaped anyway so go for it. IMHO

Neck probably just too strong. But did you test the rod to ensure it worked prior to installing it? DOA rods from suppliers are not unheard of.

Thanks for the help,



Other than the fact I still have a square/true side and I could just cut it off on my bandsaw, but yea it won't be difficult...



Yea, checked it when I first got it and then again just before I installed it.

You may be right about too strong, It is a 3 piece laminated neck so I guess that is also making it stiffer.

I guess there is no way to find out other than start carving, right?

Thanks for the help, (or maybe reassurance)

Cheers,
Bob

Bob if the rod does move the neck even a little that's an indication that the issue is not the rod. So Occam's razor suggests that you're right that the rest of the neck needs to be carved to make the truss rod's life easier.

You know too this is a good study to some extend on a related subject and that is the CF rods we see some builders installing and then we find truss rods rods that can barely move the neck and may even fail early because of the unnecessary CF.

You've provided an example of just how much wood needs to be removed before a rod is negatively impacted by the stiffness of the neck.

Anyway I digress but I suspect when you slice off some more neck things will ease up a bit for the rod.

PS: Never used the SM low profile rod but I know how it came about there were reports of the original SM red rod splitting out the back of the neck since it was taller. than most rods and left less neck wood. We had it happen once in our shop too..... Good to see they revised that or offered this alternative.

Not to be purposefully argumentative, but I ‘believe’ that I learned here on the OLF from a much wiser engineer type person that CF rods in the neck actually only added approximately 10% stiffness, which by an engineers mark made the job worth doing, but may not mean much to us in the long run. Engineers please weigh in…I bet someone with good google-fu could find the thread…

I even thought about installing CF rods. I decided against it since this is the first electric guitar neck I have done and the fact is is a ultra short scale bass. I didn't want to muck up the issue by trying to add that into the mix.



I wasn't actually aware they made this low profile rod until I started looking at what was available in the length I needed. I do know about SM rods blowing out the back of necks and figured this would be a good choice since I am profiling the neck about half way between a P Bass and a Jazz Base so it will be a bit thinner than most.



It would be interesting to hear what someone has to say that knows more about CF than I do.

Thanks again guys,
Bob

Great looking neck!
Finish carving. I suspect that being laminated and short scale, it is super stiff.

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wah
Wah-wah-wah-wah
Wah

I used CF in 5 necks. The CF inserts were 1/8” x 3/8” one on either side of the truss rod. Definitely reduces ability of the truss rod to move the neck. I think the extra stiffness helped cause a truss rod blowout on one neck and yes, it was an SM Hotrod. I never saw any particular advantage to the CF except, maybe, in a 12 string electric neck that was pretty thin. After those 5 I quit putting the CF in - kind of like semi-hemispherical fret ends, lots of work, no real advantage, and players don’t notice/care. JMHO


Steve

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Steve Smith
"Music is what feelings sound like"

Thanks, For a first neck I think it came out nice, of course I see all the buggers so...
Just started carving the back so hopefully it loosens up.




I still need to learn about making necks so CF is not something I want to throw in the mix. I try to keep things simple

The first guitar I built I did a ebony fretboard with ebony binding and semi-hemispherical fret ends... It looks beautiful... but no one notices, not even people that have played it. I doubt I would waste my time doing them again.

Cheers,
Bob

That was my experience too. The fret ends do look good though!


Steve

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Steve Smith
"Music is what feelings sound like"

From what I have seen I think I’d agree with carving the neck and seeing what happens.

One thing you could try just for fun is firmly clamping the end of the neck to a piece of wood to mimic a body attachment, support the headstock and add 10-12 lbs to the surrogate body to mimic string tension.

Obviously the frets aren’t in which would stiffen it some but if, with the truss rod loose you get a trace of relief then you will know for sure you’ll be OK when carved.

If not - well it’s a trip to the great ug-known

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It's not what you don't know that hurts you, it's what you do know that's wrong.

Went down to the shop and started carving. I band sawed out the waste and tried to adjust the truss rod but it did nothing... I figured I was this far I may as well just finish it to completion so I finished carving it out.

I was originally wanted it the shape of a 60's Jazz Bass (.0790 1st fret - 0.990 12th fret) but when I hit that mark the neck was still barely moving so I kept carving and decided for a Modern C (0.820 1st fret and 0.870 12th fret).

I don't dare go much thinner than that so that is where it will stay.

I do get movement but mostly one way, Back bow is not bad but if I try to add relief I can only get a few thousands. That is without the frets installed too...

My thought are to just finish the guitar and put this neck on and just see if the string tension will be enough to put a bit of relief into the neck.

I am wondering what you think?

Thanks for your help guys,

Cheers,
Bob

As long as fretting the neck doesn't put in a back bow you will probably be fine. If you string it up and find you don't have enough relief, tighten the strings a bit more and give it a couple of weeks to settle in.
Worse case - you can pull the frets and sand some relief into the fretboard as is sometimes done with classical guitars.

I used to use CF bars until an engineer friend of mine taught me about the engineering concept of the 'neutral axis.' In the end CF bars barely do anything at all unless you install them far away from the neutral axis but that would result in a thick neck, which by the very nature of having more wood, is even stronger making the CF bar even further unnecessary.

That and as Hesh mentioned the CF bar would just fight against the action of the truss rod.

So I stopped using them, at least till another engineer teaches me differently

Carbon fiber bars do work better the further away from the neutral axis they are, but they will still work even if they are directly on the neutral axis. That is because they are a lot stiffer than the wood that they replace. And in a guitar neck the whole neutral axis subject is sort of a moot point because how do you know where the neutral axis is? That is more complex than you would think. Plus, a guitar neck is relatively small so there is not much room to be moving the bars away from the axis in the first place.

I see a lot of posts that say either the bars don't do much good so why use them? Or they are too strong and will overcome the ability of the truss rod so why use them? Well, I still use them because they add stability to the neck and I believe they make the neck a bit more resonant. But I use relatively small bars (0.092 x 0.220 from DragonPlate) that definitely don't override the truss rod. Do they help that much? I don't know. It would be hard to prove. I would have to do an A/B comparison with testing and don't want to go to that much effort. But they are easy to install and I have them run up into the headstock, so it gives some assurance that I won't have a break near the nut. (from a retired engineer)

Thanks for that info Clay, That is one of my concerns is when I put the frets in. I may see how they fit and if the are tight I may open up the fret slots a bit to try and keep it straight.

I thought about putting relief into the neck before I put the frets in, I have done that before on a couple of guitars that gave me problems but hopefully this one will work out OK. Will see when I fret it and string it up.

@ jfmckenna & Barry Daniels,

As I said earlier I don't think I am ready to mess with CF in necks, but I can see where they would be helpful on longer scale length necks. I recently did a setup on an Ibenez Bass that could have used some CF. This thing was so floppy it was one of the hardest setups I have done. I ended up building a neck jig just for that guitar. When it was done the client was happy I got his baby back and playing but it took me twice as long to do it.

Back to the CF, One thing I was considering was putting a "liner" of ebony between the fretboard and the neck, much like a perfling to separate the 2 pieces of maple. I opted not to do it since I didn't want to throw more into the mix, but wouldn't that do the same thing as CF in the neck? I was just thinking of it as optics but it does seem it would add considerable stiffness.

Not that I need any more stiffness in THIS neck... Glad I didn't do it.

Cheers,
Bob

Actually, that would be the least effective way to use carbon fiber. A thin liner would flex up and down fairly easily, and would provide less benefit. Whereas, a rectangular bar standing on edge puts the most material further away from the neutral axis of the bar (looking at the bar without consideration of the neck). This consideration is where the neutral axis concept is most useful. A rectangular bar laying down is much less stiff than one standing up (sort of common sense).

Actually I was talking about and Ebony layer but I guess that would be even less effective than CF as far as making the neck stiffer. My thought were using it just for the looks. So maybe that would not have made it any stiffer. I don't recall ever seeing perfling lines under the fretboard but I am sure someone has done it before.

Cheers,
Bob

I have tried most all of the truss rods (and non-adjustable reinforcements) on the market in the last 50 years and I have settled on the "Martin" style 2 way rod.

These rods will pull a neck before they are carved,they are very powerful in both directions.

They are also relatively low profile.

I used a martin truss rod in my last acoustic build and had no problems. I didn't notice if it was more powerful but I haven't build enough guitars to have the experience.

Thanks for the info.

Cheers,
Bob

Also, anyone is interested I started a new build thread in the Electric Guitar and Bass section.

I don't clutter up this forum with electric guitar stuff...

Cheers,
Bob

The Martin rod is top shelf Bob, great choice.